1. Field of the Invention
This invention relates to a process for producing water-insoluble water-nondispersible polyurethane resins and sheet materials. More particularly, it relates to a process for producing polyurethane resins and microporous sheet materials having improved physical properties (such as mechanical strength and water resistance) and storage stability in addition to excellent dyeing properties such as dye-receptivity and color fastness to light, washing and rubbing.
2. Description of the Prior Art
It is known to introduce salt-like groups (such as quaternary nitrogen atoms) into polyurethane resins to impart hydrophilic properties (water-solubility or water-dispersibility), but such resins have poor physical properties (such as mechanical strength and water resistance) and therefore are not suitable as resins for producing sheet materials (such as synthetic leathers).
It has been proposed to produce sheet materials from polyurethane resins obtained by using a polymer polyol derived from an ethylenically unsaturated monomer and a high-macromolecular diol, but there may be some disadvantages such as discoloration or color change (yellowing) tendency and insufficient processability due to slow rates of solvent removal in making the sheet materials by a wet process.